In the card game of bridge, the unusual notrump is a conventional overcall showing a two-suited hand. It was originally devised by Al Roth in 1948 with Tobias Stone, to show the minor suits after the opponents opened in a major.
The convention concept is now generally extended to show the "two lowest unbid" suits. Thus, over 1♣, 2NT shows diamonds and hearts; and over 1♦, it shows clubs and hearts. In addition to succinctly describing the hand to the partner, it also deprives the opponents of bidding space, i.e. it has a preemptive effect.
When an opponent opens the bidding with 1♥ or 1♠, the immediate overcall of 2NT shows at least 5-5 in the minor suits (that is, at least five clubs and at least five diamonds) and, presumably, a weak hand (6 to 11 points). If the right hand opponent (RHO) of the partner of the 2NT bid passes, that partner is expected to bid the minor suit that he prefers at the three-level. The unusual notrump extends the principle that when the natural meaning of a bid is not generally very useful, it is profitable to agree that it means something somewhat opposite. That is, while natural notrump bids show a strong hand with balanced distribution, the unusual notrump shows a weak hand with very unbalanced distribution.
If the 2NT bidder bids again freely, then it shows a strong two suiter. To distinguish the weak and strong holdings, many partnerships agree not to use the unusual notrump for intermediate hands (about 12 to 14 points); they would simply overcall with one of their suits and show the other later if the bidding offers a chance. However, for two-suiters, many players apply losing trick count (LTC) instead of point count, as it more accurately depicts the offensive trick-taking potential of the hand. With LTC in effect, the required strength is about 4.5-7 losers, the latter only in favorable vulnerability.
Similarly, a 4NT overcall shows an extreme two suiter (usually at least 6-5, often 6-6 or 7-6) and enough trick-taking potential so that a 5-level contract can be made, or a sacrifice will likely be profitable. It shows the same two suits as 2NT would show. Note that 4NT is "unusual" only when the opponents open the bidding; otherwise, 4NT is normally played as the Blackwood convention or a quantitative invitation to 6NT.
To counteract the unusual notrump, the opening side may employ unusual vs. unusual.
Recently, the Unusual 2NT has been used in opening seat showing a 5-5 minor suited hand and 7-11 HCP. The preemptive value of the two suited hand puts pressure on the opponents to find their fits, games and slams at the three level.
When the opponents open or overcall with an Unusual 2NT, defense uses a bidding scheme which incorporates two features:
After an Unusual 2NT overcall of a major:
|1♥||2NT||Dbl||looking to penalize, no primary major fit|
|3♣||good raise in hearts (8 losers or better)|
|3♦||sound values in spades at the three level or better|
|3♥||weak raise in hearts but stretched (8½ to 9 losers)|
|3♠||six spades, not forcing|
|4♣||splinter (singleton or void in clubs) in support of hearts|
|4♦||splinter (singleton or void in diamonds) in support of hearts|
|1♠||2NT||Dbl||looking to penalize, no primary major fit|
|3♣||sound values in hearts at the three level or better|
|3♦||good raise in spades (8 losers or better)|
|3♥||six hearts, not forcing|
|3♠||weak raise in spades but stretched (8½ to 9 losers)|
|4♣||splinter (singleton or void in clubs) in support of spades|
|4♦||splinter (singleton or void in diamonds) in support of spades|
After an Unusual 2NT opening:
|2NT||Dbl||able to penalize one of the minors or 20+ HCP|
|3♣||takeout for the majors, better hearts|
|3♦||takeout for the majors, better spades|
|3♥||single suited in hearts, opening hand values|
|3♠||single suited in spades, opening hand values|
Use of the convention with insufficient strength or lengths (such as 5-4 in the minors) may lead to: